Rete testis hyperplasia with hyaline globule formation. A lesion simulating yolk sac tumor.

The presence of eosinophilic, hyaline globules in association with epithelial hyperplasia was noted in the rete testis of three patients with germ cell tumors. In the more florid examples, this proliferation formed a solid and microcystic pattern that, in association with the hyaline globules, mimicked a yolk sac tumor component. However, the bland cytologic features of the cells and the conformation to the configuration of the rete testis were keys to its reactive nature. A subsequent review of 48 testicular specimens containing well-defined areas of the rete testis showed hyaline globule formation in the rete testis or tubuli recti in 16 of 27 germ cell tumors, one of five other testicular tumors (four stromal tumors and one plasmacytoma), and none of 16 nonneoplastic cases. Many of the cases that had hyaline globules also showed epithelial hyperplasia. Further analysis demonstrated an incidence of rete testis invasion by neoplasm in cases that had hyaline globules, with or without epithelial hyperplasia, that was significantly higher (p less than 0.01) than that seen in neoplastic cases lacking hyaline globules. We concluded that this pseudoneoplastic reaction developed secondary to invasion of the rete testis by tumor. Immunostains supported the nonneoplastic nature of the proliferative lesions and indicated that the globules represented various proteins that had been absorbed from the lumen of the rete testis by the epithelial-lining cells but not successfully secreted.